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Published on: October 28, 2021
Morphological and Molecular Characterization of Meloidogyne mayaguensis Isolates from Florida
Abstract:
The discovery of Meloidogyne mayaguensis is confirmed in Florida; this is the first report for the continental United States. Meloidogyne mayaguensis is a virulent species that can reproduce on host cultivars bred for nematode resistance. The perineal patterns of M. mayaguensis isolates from Florida show morphological variability and often are similar to M. incognita. Useful morphological characters for the separation of M. mayaguensis from M. incognita from Florida are the male stylet length values (smaller for M. mayaguensis than M. incognita) and J2 tail length values (greater for M. mayaguensis than M. incognita). Meloidogyne mayaguensis values for these characters overlap with those of M. arenaria and M. javanica from Florida. Enzyme analyses of Florida M. mayaguensis isolates show two major bands (VS1-S1 phenotype) of esterase activity, and one strong malate dehydrogenase band (Rm 1.4) plus two additional weak bands that migrated close together. Their detection requires larger amounts of homogenates from several females. Amplification of two separate regions of mitochondrial DNA resulted in products of a unique size. PCR primers embedded in the COII and 16S genes produced a product size of 705 bp, and amplification of the 63-bp repeat region resulted in a single product of 322 bp. Nucleotide sequence comparison of these mitochondrial products together with sequence from 18S rDNA and ITS1 from the nuclear genome were nearly identical with the corresponding regions from a M. mayaguensis isolate from Mayaguez, Puerto Rico, the type locality of the species. Meloidogyne mayaguensis reproduced on cotton, pepper, tobacco, and watermelon but not on peanut. Preliminary results indicate the M. mayaguensis isolates from Florida can reproduce on tomato containing the Mi gene. Molecular techniques for the identification of M. mayaguensis will be particularly useful in cases of M. mayaguensis populations mixed with M. arenaria, M. incognita, and M. javanica, which are the most economically important root-knot nematode species in Florida, and especially when low (<25) numbers of specimens of these species are recovered from the soil.
Insights
The invasive root-knot nematode Meloidogyne mayaguensis is confirmed in the continental US, Florida. This virulent species reproduces on resistant cultivars, necessitating molecular identification methods for effective management.
Area of Science:
- Plant Nematology
- Molecular Diagnostics
- Agricultural Entomology
Background:
- The root-knot nematode Meloidogyne mayaguensis has been identified in Florida, marking its first detection in the continental United States.
- This species is known for its virulence, capable of reproducing on plant cultivars that are resistant to other Meloidogyne species.
- Morphological identification can be challenging due to variability and overlap with other common species like M. incognita, M. arenaria, and M. javanica.
Purpose of the Study:
- To confirm the presence of Meloidogyne mayaguensis in Florida.
- To characterize the morphological, biochemical, and molecular profiles of Florida isolates.
- To evaluate the potential of molecular techniques for accurate identification, especially in mixed populations.
Main Methods:
- Morphological analysis of perineal patterns and morphometrics (stylet length, J2 tail length).
- Enzyme electrophoresis (esterase and malate dehydrogenase activity).
- Polymerase Chain Reaction (PCR) amplification of mitochondrial DNA (COII/16S genes, repeat region) and sequencing of nuclear ribosomal DNA (18S rDNA, ITS1).
Main Results:
- Morphological characters showed variability, with male stylet and J2 tail lengths overlapping with other species.
- Enzyme analyses revealed a distinct VS1-S1 esterase phenotype and a specific malate dehydrogenase banding pattern.
- Molecular methods produced unique PCR product sizes (705 bp and 322 bp) and sequence data highly similar to the type locality isolate from Puerto Rico.
Conclusions:
- The confirmation of Meloidogyne mayaguensis in Florida poses a significant threat due to its virulence and ability to overcome resistance.
- Morphological and enzyme analyses provide some distinguishing features but can be ambiguous.
- Molecular techniques, particularly PCR and DNA sequencing, are crucial and reliable for accurate identification of Meloidogyne mayaguensis, especially in mixed populations with other economically important root-knot nematodes.
